Reactor vent control to avoid vent column breakthrough

A process for venting a gas phase polymerization reactor, comprising:

• supplying olefin monomers, a carrier gas, and a particulate catalyst to a reactor under conditions sufficient to polymerize the olefin monomers in the presence of the particulate catalyst to produce a polymer product;
• withdrawing a reactor overhead from the reactor, the reactor overhead comprising unreacted olefin monomers (C) and carrier gas (N);
• introducing a vent-bound portion of the reactor overhead from the reactor to a vent column;
• contacting the vent-bound portion of the reactor overhead with a liquid stripping medium (L) within the vent column to remove at least a portion of the unreacted olefin monomers to produce (i) a vent column overhead (G) that is rich in the carrier gas and lean in the unreacted olefin monomers and (ii) a vent column bottoms that is rich in the unreacted olefin monomers and lean in the carrier gas;
• recycling the vent column bottoms that is rich in the olefin monomers and lean in the carrier gas to the reactor;
• determining a L*N to C*G ratio, wherein L is the total liquid stripping medium flow to the vent column (kg/hr) N is the carrier gas concentration in the reactor overhead to the vent column (mol %), C is the monomer concentration in the reactor overhead to the vent column (mol %), and G is the vent column overhead gas flow (kg/hr);
• and
• controlling one or more of:
• the total liquid stripping medium flow to the vent column (L);
• the carrier gas concentration in the reactor overhead to the vent column (N);
• the monomer concentration in the reactor overhead to the vent column (C);
• and the vent column overhead gas flow (G), based on the calculated L*N to C*G ratio.